Seismic-refraction measurements on the Southeast African Continental Margin

Abstract

The results of nine seismic-refraction profiles recorded on the narrow continental shelf of southeastern Africa between Cape St. Francis and Durban are presented, together with the correlation between seismic layers and the onshore surface geology. Offshore sediment-filled depressions of a yet unknown character were found in the Durban, Port St. Johns, and Cape St. Francis vicinities, in which Cretaceous and younger sequences of velocity 1.7–3.8 km/sec rest on a Cape-Karroo substratum. The Cape and Karroo systems cannot be differentiated on the basis of seismic velocity but together form a well-defined layer of velocity 3.9–5.2 km/sec. The deepest layer measured (pre-Cape basement?) has velocities of 5.6–6.5 km/sec.